The objectives of this study are to explore the role of adenosine in the autoregulation of the normal coronary circulation in man and as an indicator of myocardial ischemia, and to examine certain questions about lactate as such an indicator. We have previously demonstrated that the product of heart rate and blood pressure is a good index of myocardial oxygen requirements during exercise in man. Work in animals has firmly established that adenosine is involved in the regulation of coronary blood flow, and has shown that concentrations of this compound and its breakdown products increase markedly in coronary sinus blood during ischemia. A considerable amount of work has been done on coronary sinus lactate concentrations as a marker of ischemic states but questions regarding its accuracy remain. Simultaneous measurements will be made of heart rate, blood pressure, and the concentrations of adenosine and its breakdown products as well as lactate and pyruvate in arterial and coronary sinus blood during a variety of manipulations of heart rate and blood pressure in animals before and after partial occlusion of the anterior descending coronary artery. In order to establish the normal relationship between these variables in man measurements will be made during diagnostic cardiac catheterization in patients with lesions that do not involve an abnormality of left ventricular loading or blood supply. The same measurements will be made in patients with abnormal left ventricular loading and during angina pectoris, and these data will be compared to the normal values in order to determine if an increase in the concentration of adenosine (and/or its metabolites) might serve as a more sensitive indicator of myocardial ischemia than measurements currently used for research or clinical purposes.